1. Field of the invention
This invention relates to a contact-type image sensor that can be used in a facsimile apparatus, an input apparatus for the reading of letters and images.
2. Description of the prior art
In conventional input apparatuses for the reading of letters and images by the use of line sensors, the manuscript is irradiated with fluorescent light or light from LED (light-emitting diode) arrays, and the reflected light from the manuscript (i.e., the information of the manuscript) reaches the sensors through optical lens, rod array lenses, or optical fibers. By shifting the manuscript or the sensors, two-dimensional information can be read from the manuscript. As such input apparatuses, there are mainly two kinds of apparatuses, one of which comprises a combination of charge coupled devices (CCD) and optical lenses, and the other of which comprises a combination of narrow strip image sensors and rod lens arrays or optical fiber arrays. Especially the latter, called contact-type image sensors, has been developed in recent years for use in a facsimile apparatus to thereby miniaturize the facsimile apparatus and reduce its production cost.
However, most of the above-mentioned contact-type image sensors are designed so that the information of the manuscript generally can reach the sensors through the rod lens arrays, resulting in a limited miniaturization of the sensors. The manuscript must be kept apart from the sensor by the conjugate length of the rod lens arrays, so the thickness of a unit of the contact-type image sensor is 20-30 mm. Moreover, since a lens system is used in the sensor, there is need for optical adjustment. and the transmittance of light is low.
In contrast, apparatuses using optical fibers instead of such a lens system do not necessitate optical adjustment, but they attain a high transmittance of light. Moreover, since there are no lenses that focus, the optical fibers can be made short, which results in a miniaturization of the apparatus. However, light that is incident upon the optical fibers at angles of a certain value or more do not attain total reflection at the interface between the wall of each of the optical fibers and the clad formed between the adjacent optical fibers, and the light reaches the adjacent optical fiber through the clad. Moreover, light that is incident upon the clad, first, reaches the sensor-side end of the bundle of optical fibers through the clad. Such light leakage reduces the quality of images. To overcome this problem, EMA (extra mural absorption)-type optical fiber arrays that are constituted by optical fibers with a light-absorbing substance disposed between the adjacent optical fibers have been proposed. When these EMA-type optical fiber arrays are applied to a contact-type image sensor, it is impossible to irradiate the manuscript with light from a light source because of the light-absorbing substances disposed among the optical fibers.